The measurement of gas flow is becoming increasingly more important in the application and control of many processes as well as in the research laboratory. One of the accepted instruments for gas flow measurement and calibration is the bubble flow meter. In the basic form of the bubble flow meter a soap film is generated from a soap solution which is propelled by the gas flow under measurement from one end of the flow meter to the other. By timing the rise of the soap film between calibrated volume marks, the volume flow is obtained. Although it is generally agreed that the bubble flow meter accuracy may be affected by changes in ambient conditions such as humidity and temperature and is dependent upon gas flow rate it is understood that these factors can be readily corrected or compensated for in a laboratory setting. This is not however, as easily done in a field setting or in a commercial process environment. Moreover, the bubble flow meter is a cumbersome and generally unwieldy instrument to use as compared to a positive displacement piston type flow meter. A reciprocating piston flow meter also provides a continuous output reading independent of operator input and with a high degree of measuring accuracy. Heretofore such a device required multiple valves and an unwieldy valving arrangement.